Re: [PATCH v3 16/23] Documentation: userspace-api: iommufd: Update vQUEUE

Nicolin Chen
2025-05-02T05:33:06Z

On Fri, May 02, 2025 at 10:50:07AM +0700, Bagas Sanjaya wrote:
> On Thu, May 01, 2025 at 04:01:22PM -0700, Nicolin Chen wrote:
> > +- IOMMUFD_OBJ_VQUEUE, representing a hardware accelerated virtual queue, as a
> > + subset of IOMMU's virtualization features, for the IOMMU HW to directly read
> > + or write the virtual queue memory owned by a guest OS. This HW-acceleration
> > + allows VM to work with the IOMMU HW directly without a VM Exit, i.e. reducing
> > + overhead from the hypercalls. Along with this vQUEUE object, iommufd provides
> > + user space an mmap interface for VMM to mmap a physical MMIO region from the
> > + host physical address space to the guest physical address space, allowing the
> > + guest OS to control the allocated vQUEUE HW. Thus, when allocating a vQUEUE,
> > + the VMM must request a pair of VMA info (vm_pgoff/size) for an mmap syscall.
> > + The length argument of an mmap syscall can be smaller than the given size for
> > + a partial mmap, but the addr argument of the mmap syscall should never offset
> > + from the returned vm_pgoff, which implies that an mmap will always start from
>
> Did you mean never be offset from returned vm_pgoff?

Yes. Will fix this.

> > + the beginning of the physical MMIO region.
> > +
>
> Confused...

Meaning that VMM should just use the given vm_pgoff as is, without
adding any offset to the vm_pgoff.

Thanks
Nicolin